This invention relates to the recovery of viscous hydrocarbons from "permeability" stratified subterranean reservoirs. More particularly, it relates to increased viscous oil production by in situ combustion with oxygen rather than air, and using the evolved nitrogen-free carbon dioxide to displace oil from another part of the reservoir.
Within stratified reservoirs are vast quantities of viscous hydrocarbons which for various reasons are not economically recoverable by conventional oil producing techniques. It has been proposed to use substantially nitrogen-free oxygen to produce oil from these stratified viscous oil reservoirs by in situ combustion. It is difficult to control combustion with pure oxygen without consuming large amounts of oil. In highly stratified reservoirs, oxygen injection causes stratifed burning mainly in the strata of highest conductivity which is also the strata of highest permeability and oil mobility. At present, it is not possible to reduce stratified flow by injection of a less mobile phase alternating or mixing with the oxygen. In situ combustion with oxygen thereby displaces only a small part of the reservoir vertical cross section.
It is an object of this invention to provide a process for increasing oil production from permeability stratified viscous oil reservoirs. An additional object of this invention is to provide an oil producing method wherein in situ combustion may be used in a way that increases oil production over the amount of oil produced by conventional in situ combustion. A further object of this invention is to increase oil production from the higher permeability, more mobile oil strata. A still further object of this invention is to increase oil production from the lower permeability, less mobile parts of stratified viscous oil reservoirs by in situ combustion.